Wobble signal detection circuit having a lowpass filter for detecting a wobble signal with reduced sampling noise

ABSTRACT

A wobble signal detection circuit is provided for an optical disk apparatus which detects a wobble signal by focusing a light beam into a spot on a pregroove on an optical disk during recording of data onto and reproduction of data from the optical disk, and includes a photodetector which detects first and second lights from first and second portions of the spot, respectively, and outputs first and second detection signals corresponding to respective power levels of the first and second detection lights. The wobble signal detection circuit includes: a sample-and-hold circuit sampling and holding the first and second detection signals output from said photodetector during the recording of the data onto the optical disk; lowpass filter means for reducing noise components of the respective first and second detection signals; and subtraction means for calculating a difference between the first and second detection signals respectively output from said lowpass filter means so as to obtain the wobble signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to wobble signal detectioncircuits and optical disk apparatus having such, and more particularly,to a wobble signal detection circuit for detecting an Absolute Time InPregroove (ATIP) signal from an optical disk such as a compact diskrecordable (CD-R) in an optical disk apparatus, and an optical diskapparatus having such.

2. Description of the Related Art

Optical disks of a direct-read-after-write type include two types:write-once and erasable. With respect to a write-once optical disk, datais written thereon mainly by focusing a light beam into a spot on a datarecording surface of the disk made from tellurium (Te) or bismuth (Bi)so as to form a pit in the disk at the location of the spot, or byfocusing a light beam into a spot on a data recording surface of thedisk made from Sb₂Se₃, TeO_(x) or a thin film of organic dye so as toalter reflectivity of the disk at the location of the spot.

A CD-R, which is a write-once optical disk, includes a number ofpregrooves as guiding tracks. The pregrooves radially wobble slightly ata center frequency of 22.05 kHz. Address information during recordingcalled ATIP is multiplexed and recorded in the pregrooves by frequencyshift keying (FSK) with a maximum deviation of ±1 kHz.

During recording of data onto and reproduction of data from the CD-R, awobble signal having the above-mentioned center frequency of 22.05 kHzis reproduced from the pregrooves to detect the ATIP information, whichis employed to confirm a recording position on the data recordingsurface of the CD-R during recording.

In other words, the ATIP information is detected in the following threemodes: a first mode wherein a wobble signal is reproduced from anunrecorded CD-R, a second mode wherein a wobble signal is reproducedfrom a CD-R during the recording, and a third mode wherein a wobblesignal is reproduced from a recorded CD-R.

FIG. 2 shows a pregroove 10 of a CD-R and a 4-part detector 12 (aphotodetector) for detecting a light beam reflected back from thepregroove 10. The 4-part detector 12 is made of four detector parts 12A,12B, 12C and 12D. In FIG. 2, the detector parts 12A and 12B form theleft half and the detector parts 12C and 12D form the right half of the4-part detector 12 with respect to a scanning direction indicated by anarrow. Conventionally, in the above-mentioned second mode, when thelight beam is focused into a spot on the pregroove 10, the detectorparts 12A, 12B, 12C, and 12D detect the reflected beam, and outputdetection signals A, B, C and D, respectively.

The detection signals are sampled and held. Then, the detection signalsA and B detected by the respective detector parts 12A and 12B are added,and the detection signals C and D detected by the respective detectorparts 12C and 12D are added.

The signal (C+D) is subtracted from the signal (A+B) so that an outputsignal (A+B)−(C+D) is obtained. Then, the output signal (A+B)−(C+D) iscompared with a reference voltage, so that a binary wobble signal isobtained.

FIG. 3A shows a waveform of the output level of the detection signal A.As shown in FIG. 3A, the power of the light beam alternately repeats awrite power state (the maximum value) and a read power state (theminimum value). A portion of the waveform of FIG. 3A including lowerpeaks is shown on an enlarged scale along the time-base direction inFIG. 3B. When the light beam is in the read power state, the detectionsignal A shown in FIG. 3B is sampled and held at sampling timingscorresponding to rising edges of a sampling pulse signal shown in FIG.3C. The sampled and held signal includes a noise generated by theabove-described sampling (a sampling noise), so that the signals (A+B)and (C+D) have waveforms shown in FIGS. 3D and 3E, respectively. Thesampling noise includes a noise generated by the swing of a read lightcaused by the transition of the beam power state from the write powerstate to the read power state. Moreover, in the case of overwriting anerasable optical disk such as a compact disk rewritable (CD-RW), thesampling noise further includes a signal component previously recordedon the disk, which appears as a noise in the sampling. The subtractionof the signal (C+D) from the signal (A+B) is performed to offset thesampling noises so that the output signal (A+B)−(C+D) has a desirablewaveform with reduced sampling noise as shown in FIG. 3F. Thereafter,the output signal (A+B)−(C+D) is compared with a reference voltage, sothat the binary wobble signal is obtained.

However, the gain and offset of a sample-and-hold circuit areinconsistent among the individual circuits, and cause errors in theoutput level of the sample-and-hold circuit. Therefore, the waveforms ofthe sampled and held detection signals A, B, C and D include thesampling noises having different levels. For example, when the samplingnoise of the signal (A+B) shown in FIG. 1A has a noise level higher thanthat of the sampling noise of the signal (C+D) shown in FIG. 1B, thesampling noises are not completely offset by the subtraction. Therefore,the sampling noise remains in the output signal (A+B)−(C+D) as shown inFIG. 1C. As the sampling is performed at higher speed, the noise levelof the sampling noise becomes higher. Therefore, when a recording speedbecomes so high that the sampling noise cannot be ignored, there arisesa problem of deterioration in performance of reproducing the ATIPinformation from the wobble signal.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a wobblesignal detection circuit and an optical disk apparatus having such inwhich the above-described disadvantage is eliminated.

A more specific object of the present invention is to provide a wobblesignal detection circuit which can effectively reduce a sampling noiseof a wobble signal when the wobble signal is reproduced during recordingso as to improve its capacity to reproduce ATIP information, and anoptical disk apparatus having such.

The above objects of the present invention are achieved by a wobblesignal detection circuit for an optical disk apparatus detecting awobble signal by focusing a light beam into a spot on a pregroove on anoptical disk during recording of data onto and reproduction of data fromthe optical disk and including a photodetector which detects first andsecond lights from first and second portions of the spot, respectively,and outputs first and second detection signals corresponding torespective power levels of the first and second lights, the first andsecond portions being formed by splitting the spot into two portions inparallel with a scanning direction, the wobble signal detection circuitincluding: a sample-and-hold circuit sampling and holding the first andsecond detection signals output from the photodetector during therecording of the data onto the optical disk; lowpass filter means forreducing noise components of the respective first and second detectionsignals, the noise components being generated by sampling the respectivefirst and second detection signals in the sample-and-hold circuit; andsubtraction means for calculating a difference between the first andsecond detection signals respectively output from the first and secondlowpass filter means so as to obtain the wobble signal.

According to the above wobble signal detection circuit, the wobblesignal is obtained by reducing the sampling noise components of thedetected signals output from the sample-and-hold circuit. Therefore, asampling noise component of the wobble signal can be reducedeffectively, thus achieving the improved capacity to reproduce ATIPinformation.

The above objects of the present invention are also achieved by a wobblesignal detection circuit for an optical disk apparatus detecting awobble signal by focusing a light beam into a spot on a pregroove on anoptical disk during recording of data onto and reproduction of data fromthe optical disk and including a photodetector which detects first andsecond lights from first and second portions of the spot, respectively,and outputs first and second detection signals corresponding torespective power levels of the first and second lights, the first andsecond portions being formed by splitting the spot into two portions inparallel with a scanning direction the wobble signal detection circuitincluding: a sample-and-hold circuit sampling and holding the first andsecond detection signals output from the photodetector during therecording of the data onto the optical disk; gain adjustment means foradjusting noise levels of noise components included in the respectivefirst and second detection signals to approximately the same level, thenoise components being generated by sampling the respective first andsecond detection signals in the sample-and-hold circuit; and subtractionmeans for calculating a difference between the first and seconddetection signals respectively output from the gain adjustment means.

The above objects of the present invention are also achieved by anoptical disk apparatus for recording data onto and reproducing data froman optical disk by detecting a wobble signal by focusing a light beam asa spot onto a pregroove on the optical disk, the optical disk apparatusincluding: a photodetector which detects first and second lights fromfirst and second portions of the spot, respectively, and outputs firstand second detection signals corresponding to respective power levels ofthe first and second lights, the first and second portions being formedby splitting the spot into two portions in parallel with a scanningdirection; and a wobble signal detection circuit, the wobble signaldetection circuit including: a sample-and-hold circuit sampling andholding the first and second detection signals output from thephotodetector during the recording of the data onto the optical disk;lowpass filter means for reducing noise components of the first andsecond detection signals, the noise components being generated bysampling the respective first and second detection signals in thesample-and-hold circuit; and subtraction means for calculating adifference between the first and second detection signals respectivelyoutput from the lowpass filter means so as to obtain the wobble signal.

The above objects of the present invention are further achieved by anoptical disk apparatus for recording data onto and reproducing data froman optical disk by detecting a wobble signal by focusing a light beaminto a spot on a pregroove on the optical disk, the optical diskapparatus including: a photodetector which detects first and secondlights from first and second portions of the spot, respectively, andoutputs first and second detection signals corresponding to respectivepower levels of the first and second lights, the first and secondportions being formed by splitting the spot into two portions inparallel with a scanning direction; and a wobble signal detectioncircuit, the wobble signal detection circuit including: asample-and-hold circuit sampling and holding the first and seconddetection signals output from the photodetector during the recording ofthe data onto the optical disk; gain adjustment means for adjustingnoise levels of noise components included in the respective first andsecond detection signals to approximately the same level, the noisecomponents being generated by sampling the respective first and seconddetection signals in the sample-and-hold circuit; and subtraction meansfor calculating a difference between the first and second detectionsignals respectively output from the gain adjustment means.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings, in which:

FIGS. 1A through 1C are diagrams showing waveforms of signals forillustrating the way a sampling noise is reduced in a conventionalwobble signal detection circuit;

FIG. 2 is a diagram showing a pregroove of a CD-R and a 4-part detector;

FIGS. 3A through 3F are diagrams showing waveforms of signals forillustrating the way the sampling noise is reduced in the conventionalwobble signal detection circuit and in embodiments of the presentinvention;

FIG. 4 is a block diagram of a wobble signal detection circuit accordingto a first embodiment of the present invention;

FIG. 5 is a block diagram of a wobble signal detection circuit accordingto a second embodiment of the present invention; and

FIG. 6 is a block diagram of an optical disk apparatus according to athird embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given, with reference to the accompanyingdrawings, of embodiments of the present invention.

FIG. 4 is a block diagram of a wobble signal detection circuit accordingto a first embodiment of the present invention.

When the light beam is focused into a spot on the pregroove 10 shown inFIG. 2, the detector parts 12A, 12B, 12C and 12D detect the reflectedbeam, and supply the detection signals A, B, C and D, respectively, to asample-and-hold circuit 14.

The sample-and-hold circuit 14 which is also supplied with a modeselection signal from a CPU 100 is switched OFF in the above-describedfirst and third modes to pass the supplied detection signals as outputs,while switched ON in the above-described second mode to sample, hold andoutput the supplied detection signals. The detection signals A and Bdetected by the respective detector parts 12A and 12B are output fromthe sample-and-hold circuit 14 to be added by an adder 16, and thedetection signals C and D detected by the respective detector parts 12Cand 12D are output from the sample-and-hold circuit 14 to be added by anadder 18.

Output signals (A+B) and (C+D) of the adders 16 and 18 are supplied tolowpass filters (LPF) 40 and 42, respectively. The LPFs 40 and 42 eachof which is also supplied with the mode selection signal from the CPU100 are switched OFF in the first and third modes to pass the suppliedsignals as outputs, and are switched ON in the second mode to cut offhigh-frequency components of the supplied detection signals havingfrequencies higher than the wobble signal frequency of 22.05±1 kHz byusing, for example, a cutoff frequency of 24 kHz. The sampling noise isa high-frequency component having a frequency of 200 kHz or higher.

In the first mode, the output signals (A+B) and (C+D) of the adders 16and 18, after passing through the LPFs 40 and 42, are supplied to asubtracter 20 via coupling capacitors C1 and C2, respectively. Thesubtracter 20 subtracts the output signal (C+D) from the output signal(A+B), and supplies a difference between the two output signals to aterminal 21 of a switch 22 as an output signal (A+B)−(C+D) because theterminal 21 of the switch 22 which is supplied with the mode selectionsignal from the CPU 100 is selected in the first mode. The output signal(A+B)−(C+D) of the subtracter 20 is supplied to a bandpass filter (BPF)24, where unnecessary frequency components of the output signal(A+B)−(C+D) are reduced. The output signal (A+B)−(C+D) is furthersupplied to a highpass filter (HPF) 26 via a coupling capacitor C3,where unnecessary frequency components of the output signal (A+B)−(C+D)are reduced. Then, the output signal (A+B)−(C+D) is compared with areference voltage V_(ref) by a comparator 28 and is output from aterminal 32 as a binary wobble signal.

On the other hand, in the third mode, the LPFs 40 and 42 are switchedOFF, and a terminal 23 of the switch 22 is selected. An output signal(A+B+RF) of the adder 16 including an RF signal reproduced from the CD-Ris supplied to a voltage-controlled amplifier (VCA) 34, while an outputsignal (C+D+RF) of the adder 18 including the reproduced RF signal issupplied to a VCA 36. An automatic gain control (AGC) circuit 35performs feedback control so that an amplitude of the output signal(A+B+RF) of the VCA 34 has a predetermined level. Similarly, an AGCcircuit 37 performs feedback control so that an amplitude of the outputsignal (C+D+RF) of the VCA 36 has the predetermined level.

A subtracter 38 subtracts the output signal (C+D+RF) of the VCA 36 fromthe output signal (A+B+RF) of the VCA 34. By this subtraction, thereproduced RF signals included in the respective signals A, B, C, and Dare offset, and the difference between the two output signals (A+B+RF)and (C+D+RF) is supplied to the terminal 23 of the switch 22 as anoutput signal (A+B)−(C+D).

As the terminal 23 is selected in the third mode, the output signal(A+B)−(C+D) is supplied to the BPF 24 for the reduction of unnecessaryfrequency components, and is further supplied to the HPF 26 via thecoupling capacitor C3 for further reduction of unnecessary frequencycomponents. Thereafter, the output signal (A+B)−(C+D) is compared withthe reference voltage V_(ref) by the comparator 28 and is output fromthe terminal 32 as the binary wobble signal.

Further, in the second mode, the sample-and-hold circuit 14 and the LPFs40 and 42 are switched ON, and the terminal 21 of the switch 22 isselected. As shown in FIG. 3A, the power of the light beam alternatelyrepeats the write power state (the maximum value) and the read powerstate (the minimum value). When the light beam is in the read powerstate, the sample-and-hold circuit 14 samples and holds the detectionsignals at the sampling timings corresponding to the rising edges of thesampling pulse signal as previously described with reference to FIGS. 3Band 3C.

The output signals from the sample-and-hold circuit 14 each include thesampling noise, so that the output signals (A+B) and (C+D) of the adders16 and 18 have the waveforms shown in FIGS. 3D and 3E, respectively.However, as the sampling noises of the output signals (A+B) and (C+D)are reduced by the LPFs 40 and 42, the subtracter 20 calculates thedifference between the output signals (A+B) and (C+D), and outputs thesignal (A+B)−(C+D) having the waveform with reduced sampling noise asshown in FIG. 3F.

As the terminal 21 is selected, the output signal (A+B)−(C+D) issupplied to the BPF 24 for the reduction of unnecessary frequencycomponents, and is further supplied to the HPF 26 via the couplingcapacitor C3 for further reduction of unnecessary frequency components.Thereafter, the output signal (A+B)−(C+D) is compared with the referencevoltage V_(ref) by the comparator 28 and is output from the terminal 32as the binary wobble signal.

As described above, the sampling noise included in the wobble signal canbe reduced effectively, and the capacity to reproduce the ATIPinformation during recording, particularly, during high-speed recording,can be improved.

According to this embodiment, the subtracter 20 is connected between theBPF 24 and each of the LPFs 40 and 42. This is because, if thesubtracter 20 were connected between the adders 16 and 18 and the LPFs40 and 42, the subtraction by the subtracter 20 may shift thefrequencies of the sampling noises to a lower frequency band, and thesampling noises may pass through the LPFs 40 and 42. A LPF similar tothe LPFs 40 and 42 can be connected, for each of the output signals ofthe sample-and-hold circuit 14, between the sample-and-hold circuit 14and each of the adders 16 and 18.

FIG. 5 is a block diagram of a wobble signal detection circuit accordingto a second embodiment of the present invention. In FIG. 5, the sameelements as those of FIG. 4 are referred to by the same numerals. InFIG. 5, the detection signals A, B, C, and D detected by the respectivedetector parts 12A, 12B, 12C, and 12D of FIG. 2 are supplied to thesample-and-hold circuit 14.

The sample-and-hold circuit 14 which is also supplied with the modeselection signal from the CPU 100 is switched OFF in the above-describedfirst and third modes to pass the supplied detection signals as theoutputs, while switched ON in the above-described second mode to sample,hold and output the supplied detection signals. The detection signals Aand B detected by the respective detector parts 12A and 12B are outputfrom the sample-and-hold circuit 14 to be added by the adder 16, and thedetection signals C and D detected by the respective detector parts 12Cand 12D are output from the sample-and-hold circuit 14 to be added bythe adder 18.

The output signals (A+B) and (C+D) of the adders 16 and 18 are suppliedto gain adjustment circuits 50 and 52, respectively. The gain adjustmentcircuits 50 and 52 each of which is supplied with the mode selectionsignal from the CPU 100 are switched OFF in the first and third modes topass the supplied signals as outputs, and are switched ON in the secondmode.

For example, the gain adjustment circuits 50 and 52 are adjusted bymonitoring the output of the comparator 28 using a jitter meter in themanufacturing process, so that the jitter of the output of thecomparator 28 is minimized. Therefore, the output levels of the gainadjustment circuits 50 and 52, which include errors caused by theinconsistent gains and offsets of the sample-and-hold circuit 14 and theadders 16 and 18, are set at approximately the same level.

In the first mode, the output signals (A+B) and (C+D) of the adders 16and 18, after passing through the gain adjustment circuits 50 and 52,are supplied to the subtracter 20 via the coupling capacitors C1 and C2,respectively. The subtracter 20 subtracts the output signal (C+D) fromthe output signal (A+B), and supplies the difference between the twooutput signals to the terminal 21 of the switch 22 as the output signal(A+B)−(C+D) because the terminal 21 of the switch 22 which is suppliedwith the mode selection signal from the CPU 100 is selected in the firstmode. The output signal (A+B)−(C+D) from the subtracter 20 is suppliedto the BPF 24, where unnecessary frequency components of the outputsignal (A+B)−(C+D) are reduced. The output signal (A+B)−(C+D) is furthersupplied to the HPF 26 via the coupling capacitor C3, where unnecessaryfrequency components of the output signal (A+B)−(C+D) are reduced. Then,the output signal (A+B)−(C+D) is compared with the reference voltageV_(ref) by the comparator 28 and is output from the terminal 32 as thebinary wobble signal.

On the other hand, in the third mode, the gain adjustment circuits 50and 52 are switched OFF, and the terminal 23 of the switch 22 isselected. The output signal (A+B+RF) of the adder 16 including thereproduced RF signal is supplied to the VCA 34, while the output signal(C+D+RF) of the adder 18 including the reproduced RF signal is suppliedto the VCA 36. The AGC circuit 35 performs feedback control so that theamplitude of the output signal (A+B+RF) of the VCA 34 has thepredetermined level. Similarly, the AGC circuit 37 performs feedbackcontrol so that the amplitude of the output signal (C+D+RF) of the VCA36 has the predetermined level.

The subtracter 38 subtracts the output signal (C+D+RF) from the VCA 36from the output signal (A+B+RF) from the VCA 34. By this subtraction,the reproduced RF signals included in the respective detection signalsA, B, C and D are offset, and the difference between the two outputsignals (A+B+RF) and (C+D+RF) is supplied to the terminal 23 of theswitch 22 as the output signal (A+B)−(C+D). As the terminal 23 isselected in the third mode, the output signal (A+B)−(C+D) is supplied tothe BPF 24 for the reduction of unnecessary frequency components, and isfurther supplied to the HPF 26 via the coupling capacitor C3 for furtherreduction of unnecessary frequency components. Thereafter, the outputsignal (A+B)−(C+D) is compared with the reference voltage V_(ref) by thecomparator 28 and is output from the terminal 32 as the binary wobblesignal.

Further, in the second mode, the sample-and-hold circuit 14 and the gainadjustment circuits 50 and 52 are switched ON, and the terminal 21 ofthe switch 22 is selected. As shown in FIG. 3A, the power of the lightbeam alternately repeats the write power state (the maximum value) andthe read power state (the minimum value). When the light beam is in theread power state, the sample-and-hold circuit 14 samples and holds thedetection signals at the sampling timings corresponding to the risingedges of the sampling pulse signal as previously described withreference to FIGS. 3B and 3C.

The output signals from the sample-and-hold circuit 14 each include thesampling noise, so that the output signals (A+B) and (C+D) of the adders16 and 18 have the waveforms shown in FIGS. 3D and 3E, respectively.However, as the noise levels of the sampling noises are adjusted toapproximately the same level by the gain adjustment circuits 50 and 52,the subtracter 20 calculates the difference between the output signals(A+B) and (C+D), and outputs the signal (A+B)−(C+D) having the waveformwith reduced sampling noise as shown in FIG. 3F.

As the terminal 21 is selected, the output signal (A+B)−(C+D) issupplied to the BPF 24 for the reduction of unnecessary frequencycomponents, and is further supplied to the HPF 26 via the couplingcapacitor C3 for further reduction of unnecessary frequency components.Thereafter, the output signal (A+B)−(C+D) is compared with the referencevoltage V_(ref) by the comparator 28 and is output from the terminal 32as the binary wobble signal.

As described above, the sampling noise included in the wobble signal canbe reduced effectively, and the capacity to reproduce the ATIPinformation during recording, particularly, during high-speed recording,can be improved.

According to this embodiment, the two gain adjustment circuits 50 and 52are provided. However, the number of the gain adjustment circuits is notlimited to two. The gain adjustment circuits 50 and 52 can be replacedby either one of the two, or a gain adjustment circuit similar to thegain adjustment circuits 50 and 52 can be provided for each of the fouroutput signals from the sample-and-hold circuit 14.

FIG. 6 is a block diagram of an optical disk apparatus according to athird embodiment of the present invention. According to FIG. 6, anoptical disk 60 (a CD-R) is actuated by a spindle motor (not shown) torotate about a spindle shaft 62. A microcomputer 64, which correspondsto the CPU 100 in FIGS. 4 and 5, supplies a command signal to a servocircuit 66 based on a write/read command supplied from a host apparatus(not shown). The servo circuit 66 controls the rotation of theabove-mentioned spindle motor so as to maintain a constant linearvelocity (CLV). The servo circuit 66 also controls the rotation of athread motor (not shown) of an optical pickup 68 so that the opticalpickup 68 is moved to a desired track of the optical disk 60. The servocircuit 66 further controls the focusing and tracking of the opticalpickup 68.

A laser beam emitted from the optical pickup 68 is reflected from arecording surface of the optical disk 60 to be detected by the opticalpickup 68. A read signal obtained by the optical pickup 68 is suppliedto a reproduction circuit 70 for wave shaping. The read signal outputfrom the reproduction circuit 70 is then supplied to the servo circuit66 and, at the same time, to a wobble signal detection circuit 72, inwhich a wobble signal is detected. By demodulating the wobble signalusing FSK in an ATIP decoder 74, ATIP information is obtained from thewobble signal, and is supplied to the microcomputer 64 and to the servocircuit 66. The read signal is demodulated in the reproduction circuit70, and is supplied to a decoder 76 to be decoded using cross-interleaveReed-Solomon code (CIRC) and be subjected to an error correction beforebeing output therefrom as reproduced data.

The microcomputer 64 generates a recording power control signal, whichis converted into an analog signal in a D/A converter 82 to be suppliedto a recording circuit 84 as a recording power control voltage. A signalto be recorded is input to an encoder 86 and encoded using CIRC based onthe control of the microcomputer 64, and is supplied to the recordingcircuit 84.

The recording circuit 84 modulates, using eight to fourteen modulation(EFM), a signal supplied from the encoder 86 during recording. Therecording circuit 84 controls the recording power in accordance with therecording power control voltage, depending on the modulated signal, andthe recording power is supplied to a laser diode (LD) of the opticalpickup 68 so that the LD is driven. As a result, the laser beam isprojected on the optical disk 60, and the signal is recorded thereon.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

For example, according to the above-described embodiments, the presentinvention is applied to the CD-R, which is a write-once optical disk.However, the recording medium is not limited to the CD-R, and anerasable disk can replace the CD-R if an ATIP signal is includedtherein.

The present application is based on Japanese priority patent applicationNo. 11-266090 filed on Sep. 20, 1999, the entire contents of which arehereby incorporated by reference.

1. A wobble signal detection circuit for an optical disk apparatus whichdetects a wobble signal by focusing a light beam into a spot on apregroove on an optical disk during recording of data onto andreproduction of data from the optical disk, and includes a photodetectorwhich detects first and second lights from first and second portions ofthe spot, respectively, and outputs first and second detection signalscorresponding to respective power levels of the first and second lights,the first and second portions being formed by splitting the spot intotwo portions in parallel with a scanning direction, said wobble signaldetection circuit comprising: a sample-and-hold circuit sampling andholding the first and second detection signals output from saidphotodetector during the recording of the data onto the optical disk;lowpass filter means for reducing noise components of the respectivefirst and second detection signals, the noise components being generatedby sampling the respective first and second detection signals in saidsample-and-hold circuit; and subtraction means for calculating adifference between the first and second detection signals respectivelyoutput from said lowpass filter means so as to obtain the wobble signal.2. The wobble signal detection circuit as claimed in claim 1, wherein:said photodetector includes first, second, third, and fourth detectorparts detecting corresponding light beams reflected from the spot andoutputting respective detection signals corresponding to power levels ofthe detected light beams, the photodetector being split along thescanning direction into first and second half portions, the first halfportion being split along a direction perpendicular to the scanningdirection into the first and second detector parts and the second halfportion being split along the direction perpendicular to the scanningdirection into the third and fourth detector parts; and saidsample-and-hold circuit samples and holds the detection signals outputfrom the first, second, third, and fourth detector parts of saidphotodetector during the recording of the data onto the optical disk,said wobble signal detection circuit further comprising adding means towhich the detection signals output from the first, second, third andfourth detector parts are supplied from said sample-and-hold circuit sothat the detection signals output from the first and second detectorparts are added to be supplied to said lowpass filter means, and thedetection signals output from the third and fourth detector parts areadded to be supplied to said lowpass filter means.
 3. An optical diskapparatus for recording data onto and reproducing data from an opticaldisk by detecting a wobble signal by focusing a light beam into a spoton a pregroove on the optical disk, said optical disk apparatuscomprising: a photodetector which detects first and second lights fromfirst and second portions of the spot, respectively, and outputs firstand second detection signals corresponding to respective power levels ofthe first and second lights, the first and second portions being formedby splitting the spot into two portions in parallel with a scanningdirection; and a wobble signal detection circuit, said wobble signaldetection circuit comprising: a sample-and-hold circuit sampling andholding the first and second detection signals output from saidphotodetector during the recording of the data onto the optical disk;lowpass filter means for reducing noise components of the respectivefirst and second detection signals, the noise components being generatedby sampling the respective first and second detection signals in saidsample-and-hold circuit; and subtraction means for calculating thedifference between the first and second detection signals respectivelyoutput from said lowpass filter means so as to obtain the wobble signal.4. The optical disk apparatus as claimed in claim 3, wherein: saidphotodetector includes first, second, third, and fourth detector partsdetecting corresponding light beams reflected from the spot andoutputting respective detection signals corresponding to power levels ofthe detected light beams, the photodetector being split along thescanning direction into first and second half portions, the first halfportion being split along a direction perpendicular to the scanningdirection into the first and second detector parts and the second halfportion being split along the direction perpendicular to the scanningdirection into the third and fourth detector parts; and saidsample-and-hold circuit samples and holds the detection signals outputfrom the first, second, third, and fourth detector parts of saidphotodetector during the recording of the data onto the optical disk,said wobble signal detection circuit further comprising an addingcircuit to which the detection signals output from the first, second,third and fourth detector parts are supplied from said sample-and-holdcircuit so that the detection signals output from the first and seconddetector parts are added to be supplied to said lowpass filter means,and the detection signals output from the third and fourth detectorparts are added to be supplied to said lowpass filter means.